EARLIER this month Tokelau, a trio of tiny coral atolls midway between New Zealand and Hawaii, laid claim to be the world's first fully renewable energy nation.

It's a boast with some foundation, though Tokelau is actually a dependency of New Zealand. For most of the time, 4000-plus solar photovoltaic (PV) panels provide all the electricity its 1400 residents need.

Diesel generators have been required on only a couple of days since the first atoll's system was switched on in August, and even these may go if a proposed coconut biofuel plant gets built.

Batteries keep the lights on at night, and are perhaps the most surprising component of the otherwise high-tech array. Nestled among the coconut palms and shiny solar panels are bungalows containing 1344 giant lead-acid batteries weighing a combined 257 tonnes.

''It's the oldest [battery] technology there is,'' said Philippe McCracken, a project engineer with Australian renewable energy consultants IT Power, who helped install the $5.9 million system. ''It's why we use it - it's reliable.''

The use of the century-old technology is a necessity. If something goes wrong, it takes a maintenance crew five hours to fly from Sydney to Samoa, and another 24 on a boat to Tokelau. The boat sails roughly once a fortnight.

Tokelau's energy set-up may seem anachronistic, but it is one of the few places with deployed battery storage at grid-scale.

A more sophisticated and affordable version of this technology remains one of the barriers to renewable energy being deployed on a much larger scale.

Only now are alternative battery technologies emerging from the laboratories despite decades of research in how to store energy.

''Storage is expensive no matter what technology you're using,'' Mr McCracken said. ''It's sort of the holy grail of the renewable energy world to have a cheap form of storage.''

Issue heats up

Finding a way to cut the cost of storage - whether in the form of hydropower reservoirs, nickel metal hydride batteries used in electric vehicles, or frontier technologies using vanadium or zinc bromine batteries - is one of the hottest issues in energy.

On King Island, Hydro Tasmania will soon install advanced lead-acid batteries developed by CSIRO, known as UltraBatteries, to store excess wind energy, with the aim of slashing the island's diesel bill by two-thirds. It may expand to nearby Flinders Island and beyond if the project succeeds.

The UltraBattery, now owned by US firm East Penn, combines lead-acid battery technology with a super-capacitor to boost performance. They remain large. The storage array on King Island will require 1440 units - almost one per King Islander - weighing 170 tonnes in total.

But the most pressing need for energy storage - and therefore, the biggest potential market - is smoothing out periods of intermittent supply within electricity grids, rather than long-term banking of reservoirs of energy.

Imre Gyuk, director of the US government's energy storage program, said that just to allow for shifting energy flows as wind speeds change or clouds block the sun grid operators need a buffer of about 10 per cent. ''So for every 10 megawatts of new renewables that you put into the system, you need either 1 megawatt of storage or demand response,'' he said during a visit to Australia last week.

Becoming viable

Proponents of emerging storage options say a slew of new products that could help solve those grid issues are at near-commercial stage.

''We are sort of at the same point, perhaps, where PV was about five to 10 years ago,'' said Professor Tony Vassallo, who works in sustainable energy development at the University of Sydney. ''What we're finding is the technology is available, the cost of electricity is going up, and it's now becoming viable to use storage in grids to manage peak demand, to manage the integration of intermittent renewables.''

The University of New South Wales' Professor Maria Skyllas-Kazacos - a pioneer with her work on vanadium redox batteries - said new technologies may be cost-competitive within about five years.

Short-term smoothing of wind and PV power may work best with lithium-ion and the UltraBattery, while zinc bromine and vanadium redox are leading contenders when storage is required for several hours or for overnight use, she said.

If energy performance is one issue, another is safety. Since the aim is to cram as much energy as possible into a small volume, experts warn batteries can become ''small bombs''.

Several years ago a researcher in Sydney charged a lithium battery being tested overnight at the wrong voltage. ''The whole thing exploded and almost blew a hole in the wall,'' Professor Skyllas-Kazacos told a conference last week.

''There was also a fire at a sodium-sulphur battery installation in Hawaii last year and this was due to the use of molten sodium and molten sulphur in this system that are both extremely hazardous,'' she said.

Professor Vassallo said battery developers will manage those risks as they have for other energy sources, such as petrol in cars.

''People forget that they drive around with 60 litres of highly flammable solvent under their seat,'' he said.

Market force

Alex Wonhas, director of the CSIRO's Energy Transformed Flagship, said he doubted technology alone would deliver the breakthrough needed.

''I think it's more a market issue,'' he said. ''The game-changer would be to appropriately value the network benefit that storage could create.''

Whether the electricity market will soon start to reward those deploying storage at home or across the grid may become clearer on Thursday, when the Australian Energy Market Commission releases a report that in part will look at what changes can be made to give consumers more choice in in taking steps to cut costs and reduce usage at peak times.

Tokelau may be on the sidelines of that debate but it has keen interest in the shift away from fossil-fuel based energy, a major source of greenhouse gas emissions blamed for heating the planet and raising sea levels.

The atolls are barely a few metres above the normal high tide and rising sea levels are already affecting life. A report out Wednesday, released at the global climate talks in Doha, found sea levels are rising 60 per cent faster than previous projections.

A freshwater marsh, formerly used to irrigate the Tokalau’ans’ taro crop is no longer in use.

“Over the years, it’s become brackish and they can’t plant their crops there any more,” said IT Power’s Mr McCracken. “The water’s no good.”